The City at the Center of the Cosmos

Robots and lasers are uncovering an ancient, sacred geography.

Some 48 kilometers north of Mexico City, in the Basin of Mexico, towers the Pyramid of the Sun at Teotihuacán. This massive 71-meter…By Brian Fagan

Some 48 kilometers north of Mexico City, in the Basin of Mexico, towers the Pyramid of the Sun at Teotihuacán. This massive 71-meter high structure makes you feel like a speck of dust in the presence of the gods. And that is exactly what the builders intended. Those who dwelt at Teotihuacán lived at the heart of a vast sacred landscape. The city itself covered more than 21 square kilometers, and it dominated the basin and the surrounding highlands. By 100 A.D., at least 80,000 people lived there. And between 200 and 750 A.D., Teotihuacán’s population swelled to more than 150,000. At the time, it was as big as all but the largest cities of China and the Middle East.

Archaeologists have worked there for nearly a century. They’ve learned that Teotihuacán was a vast symbolic landscape of artificial mountains, foothills, caves, and open spaces that replicated the spiritual world. Over a period of more than eight centuries, the Teotihuacános built 600 pyramids, 500 workshop areas, a huge marketplace, 2,000 apartment complexes, and several squares or plazas.

Cosmology as geography: A view from the Pyramid of the Moon toward the Pyramid of the Sun.DEA / ARCHIVIO J. LANGE / Contributor / Getty Images

At some point, the city’s rulers decided to rebuild much of the city. They constructed standardized, walled residential compounds, probably to replace crowded urban areas. Some of these housed artisans and their workshops. Others were military quarters. Foreigners from the Valley of Oaxaca and lowland Veracruz on the coast of the Gulf of Mexico lived in their own neighborhoods, which are identified by distinctive pottery styles.

Everything followed a grid plan, with the streets all running at right angles to one another. Bisecting the city in a north–south direction was a wide avenue, known ever since the Spanish Conquest as the Avenue of the Dead.

The great Pyramids of the Sun and the Moon dominate the avenue’s north end. Between 150 and 325 A.D., the city’s rulers remodeled the Pyramid of the Sun into its present form, enlarged the Pyramid of the Moon and extended the Avenue of the Dead more than a mile southward to include the Ciudadela—the city’s new political and religious center. Until recently, not much was known about this impressive structure. Then in 2003, the National Institute of Anthropology and History in Mexico City embarked on an ambitious, long-term program to investigate and preserve the Ciudadela temples. The project continues to this day, and in recent years there have been some spectacular discoveries.

Chávez and his colleagues were the first people to enter the tunnel for 1,800 years.

The Ciudadela complex is enormous, with high walls and a large courtyard. As many as 100,000 people could gather within the enclosed space for major public ceremonies. The Temple of Quetzalcoatl, the ancient feathered serpent god of Central American civilization, lies within the enclosure, facing the open space. This is a six-level stepped pyramid with a huge stairway running up it, the steps of which form small terraces. Heads of feathered serpents and a snake-like creature, perhaps a war serpent, decorate the faces of these terraces. Reliefs of the feathered serpent also appear under each row of heads, together with a depiction of water. The entire temple was painted blue and carved seashells provided decoration. What the color and the heads and other decorations signified is unknown, but it seems possible that they represented the cosmos (the universe) at the time of creation—a calm ocean.

The excavators started from scratch, working on a temple that had been badly damaged, partly by rain and high groundwater levels, and partly by large numbers of tourists. In 2004, the World Monuments Fund provided money and technical assistance for the conservation of this unique structure.

Excavations by Mexican archaeologists in the large plaza beside the Temple of Quetzalcoatl uncovered the remains of several structures that by 200 A.D. had been built on what was originally farmland. These had formed the first religious complex. One of the structures was more than 120 meters long and may have served as a court for ceremonial ball games (an ancient ritual that could include the sacrifice of the losers). The architects of Quetzalcoatl’s temple destroyed these buildings when they erected the Ciudadela in its present form.

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The open space in front of the temple in the Ciudadela was designed to be flooded with water to form a reflective surface. It was a kind of “water mirror,” a symbolic reflection of the calm sea that existed before the creation of the world and humans. According to ancient origin myths, a Sacred Mountain is said to have risen from this watery mass at the beginning of time. All this suggests that the Ciudadela was the setting for rituals in which myths about the creation of the world were re-enacted.

Heavy rains in 2003 revealed a depression and a deep hole in the ground in front of the steps of the Quetzalcoatl temple platform. Now, after years of work, archaeologists explored under the temple for the first time. One—Sergio Gómez Chávez—was lowered by rope through the small opening. He reached solid ground almost 14 meters down and found an underground tunnel leading east toward the Temple of the Feathered Serpent and west toward the center of the great plaza. The tunnel was mostly filled with earth and carved stone blocks, put there by the Teotihuacános.

To clear and explore the underground passageway required careful planning. In 2004, 2005, and 2010, before they went underground, Chávez and his colleagues used ground-penetrating radar to plot the passage from the surface. This suggested that the tunnel was between 100 and 120 meters long, with the eastern end at the center of the Temple of the Feathered Serpent. The radar plots hinted at a large chamber in the middle of the tunnel and an even larger one at the eastern end. They also provided a way of planning the underground exploration.

The investigation was based on a series of carefully thought-out assumptions. First, the researchers assumed that Teotihuacán was a replica of its inhabitants’ vision of the universe, with three levels formed by the gods—the heavens, the earth, and the underworld. The horizontal plane represented north, east, south, and west. And the corners of the plane were the corners of the world.

Second, the excavators assumed that the Temple of the Feathered Serpent symbolized the Sacred Mountain of the creation, thought to have emerged from the calm sea at the beginning of time. The temple stood on a sacred spot, the center of the world. Here you could communicate with the different layers of the cosmos.

Third, they assumed that a sacred cave, thought to lie below the Sacred Mountain, was the place of entry into the underworld. This was inhabited by the gods and by the creative forces that maintained the cosmos. The tunnel, which was partly explored by Chávez with radar, was a symbolic representation of this underworld. According to ancient cosmology (study of the universe), the underworld had its own sacred geography.

Finally, they assumed that the underground passage was visited frequently, but only by those individuals involved in rituals that bolstered their power. This was where such people acquired spiritual powers, by performing ritual acts. Some objects from the rituals, perhaps even the remains of those who gave and received gifts, might be present in the tunnel.

Everything had a ritual significance—even the way the tunnel had been dug below the natural water table, in order to re-create the watery environment of the underworld.

The underground excavations started in 2006 and continue to this day. Chávez began in an area of about 100 square meters, where he thought the main entrance to the tunnel once lay. A pit covering 5 square meters lay about 2 meters below the surface. This provided access to a tunnel leading toward the pyramid.

Artifacts and stone blocks filled the narrow passageway, making it hard to plan the excavation. Chavez turned once again to remote sensing, this time underground. This time he used a laser scanner—a highly accurate measuring device—to plan the next stage of the work. A first attempt recorded 37 meters of the tunnel. Another scan in 2011 reached 73 meters. These measurements confirmed that there was indeed a long tunnel leading toward the pyramid, but its precise overall length was still uncertain.

Next, Chávez used a small remote-controlled robot, equipped with video cameras. This penetrated 37 meters into the tunnel to test for stability and potential working conditions. This helped excavation of the previously laser-scanned segment of the passageway. In 2013, a more sophisticated robot with an infrared camera and a miniature laser scanner managed to get through the last, previously inaccessible 30 meters of the tunnel. This was no easy task. Ancient Aztec visitors had visited the tunnel on many occasions to leave offerings in the tunnel. To do so, they had to make their way through, and often partially demolish, more than 20 thick walls that had blocked it. In the end, the entire space was filled with offerings. Chávez and his colleagues were the first people to enter the tunnel for 1,800 years.

By 2013, the excavation extended 65 meters into the tunnel. Two side chambers had come to light. Their walls and roofs had been finished using a powder created from a metallic mineral, and they shone like a starry night or like sparkling running water. One of the chambers contained more than 400 mineral metal balls. These objects remain a complete mystery. After the two side chambers, the tunnel’s depth gradually increased by a further 2 meters and it continued for 35 meters to the east. At the end were three chambers, facing north, south, and east.

More than 75,000 objects have emerged from the excavation, which now extends over 103 meters of tunnel and to a depth of up to 17 meters below the surface. Thousands of offerings have come from the dig, among them minerals such as jade, serpentine, and turquoise; obsidian (volcanic glass); and liquid mercury. Hundreds of clay vessels and mirrors made from polished pyrite (a shiny mineral often confused with gold) lay alongside seashells. Dozens of unusual clay vessels have come to light, along with rubber balls, necklaces, wooden objects, and fragments of human skin.

What do all these finds mean? Chávez and his teammates argue that the Ciudadela re-created the sacred geography of the cosmos and the work of the gods. The Pyramid of the Feathered Serpent symbolized the Sacred Mountain, which served as a link between the various layers and regions of the cosmos. The underground tunnel and caves beneath the temple transformed space on earth into a wet, cold, dark underworld. It was there that rulers acquired the supernatural power to govern. The tunnel under the pyramid took the city’s rulers into the underworld. Vanishing under the earth suggested that they could visit this unknown world, an act that gave them the ability to communicate with the forces of the supernatural realm. The Ciudadela was where everyone in the great city participated in public ceremonies that marked major events in the ritual calendar. It was there, too, that the architects attempted to create the entrance to the underworld.

The on-going Ciudadela project is no fast-moving search for precious objects, but rather a systematic, painstaking analysis of the meaning of the objects in the tunnel. Everything had a ritual significance—including the way the tunnel had been dug below the natural water table, in order to re-create the watery environment of the underworld. The last 30 meters of the tunnel had been made even deeper, so that they were always filled with water, representing the sacred water of the creation.

Investigations at Teotihuacán began a century ago, but the city is so enormous that they have hardly scratched the surface. The current emphasis is on tunneling—not only at the Ciudadela, but also under the Pyramids of the Sun and the Moon. Here further tunnels and rich offerings, as well as sacrificial victims, will help decipher the complex symbolism of one of the greatest cities in history.

Brian Fagan is a professor emeritus of anthropology at the University of California, Santa Barbara. He is the author of Fish on Friday, The Little Ice Age, The Long Summer, and the New York Times bestseller The Great Warming.

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